Experimental Study On Progressive Collapse-resisting Performance Of Prestressed Fabricated PC Frame After The Removal Of The Exterior Column

The development and application of precast structure have been vigorously promoted in China for the past few years,whereas precast concrete structure is more prone to progressive collapse subjected to accidental load comparing with cast-in-place reinforced concrete structure.Most of the existing studies on progressive collapse resisting of structures focused on cast-in-place structure,and the studies of the progressive collapse resisting of precast structure are relatively scarce.A series of related previous studies conducted on the prestressed fabricated PC frame by the research group showed that it has good seismic behavior and reliable joint connection performance.Therefore,based on the support of the National Natural Science Foundation of China,this paper made a further study on the progressive collapse resisting of the prestressed fabricated PC frame.This paper relies on the support of the National Natural Science Foundation of China.In this paper,a two-story two-span prefabricated fabricated structure is tested to remove the side columns,and then the continuous collapse resistance of the prefabricated prestressed concrete frame is studied when the side columns are damaged.The following is the main research content and results of this paper.(1)A two-story two span prefabricated fabricated structure plane frame was tested under vertical load.The stress mechanism and failure mode of the frame after removing the bottom side column are known through the test.The relation curve of bearing capacity side column displacement is obtained.And through the analysis of the test data such as the horizontal displacement of the top of the column,the strain of the steel bar and the rotation angle,the continuous collapse resistance and mechanism of the structure are discussed.(2)By analyzing the load-displacement curve,the horizontal displacement of the frame and the beam-column rotation angle,the stress process of the frame is roughly divided into the elastic stage,the elastic-plastic stage,the plastic hinge development stage and the collapse stage.In the stage of small deformation,the bearing mechanism of the frame is "beam mechanism",and the frame column tends to incline outwards;in the stage of collapse,the axial tension produced by the prestressed steel strand inside the frame provides a large bearing capacity for the structure.Ordinary rebar is not penetrated at the beam-column joint,so it is not subjected to tensile yielding,and the contribution of the bearing capacity is small,but it has a certain help to suppress the cracking of the frame beam.(3)The finite element analysis software abaqus is used to numerically analyze the test frame,and the model building process is introduced in detail.The simulation results are compared with the test results.The load-displacement curves and failure modes are in good agreement with the actual test conditions.The model has high reliability and can reflect the stress performance of the specimen at each loading stage.(4)Through the analysis of the test results and relevant data,it is shown that the main source of deformation of the structure before reaching the bearing capacity limit is the plastic hinge rotation of the middle column near the end section of the failure edge column beam.At this time,the failure of the structure is mainly controlled by the beam end section of the middle column near the failure side column.In this paper,a simplified structural resistance analysis model is proposed,and the calculation method of the collapse resistance ultimate bearing capacity of the structure is derived,which provides a reference for the establishment of relevant design methods.(5)According to the study of the failure state of the collapse point in the test,the failure of the structure is mainly concentrated near the beam hinge.A simplified calculation model is established to calculate the displacement of the collapse critical point of the structure.(6)Based on two hypotheses,an energy evaluation model without considering the favorable damping effect is established.The dynamic response curve of the structure under sudden vertical load is obtained by the results under static load.This simplified analysis method can effectively evaluate the non-linear dynamic response of the structure,and can be used conservatively as the judgment basis of whether the structure collapses.The maximum dynamic load point obtained based on the energy method can be used as the judgment basis of whether the prefabricated structure collapses under the dynamic load.